A critical hub for transportation and economic growth, the $288 million Johnson County Gateway project in Kansas will wrap up this year, providing residents and commerce safer and more efficient travel through the western outskirts of Kansas City.

"This is the busiest interchange in the state of Kansas," says Paul Gripka, Kansas Department of Transportation (KDOT) Project Director. "It was getting to the point there was not enough capacity. When you increase capacity and keep traffic moving, it improves safety."

About 230,000 vehicles pass through the intersection daily. With heavy traffic, drivers experienced increased difficulty merging and changing lanes to get on and off the ramps. KDOT added collector-distributor roads to improve safety.

KDOT hired HNTB of Overland Park, Kansas, as a consultant to assist with the concept, the design-build process and management of the project, and selected Gateway Interchange Constructors (GIC) to design and build the second phase of the Gateway Project from three short-listed teams. GIC is a joint venture between Clarkson Construction of Kansas City, Missouri, and Kiewit Infrastructure Co. of Omaha, Nebraska.

GIC hired HDR with an office in Olathe, Kansas, and George Butler Associates of Kansas City, Missouri, for the design. It also retained Lamb-Star of Plano, Texas, for quality assurance.

The project included widening east- and westbound Interstate 435, widening of northbound Interstate 35, a new eastbound collector-distributor road to I-35, new flyover ramps at I-435 and I-35, reconstruction of K-10 including a new flyover ramp,  two diverging diamond interchanges and widening of some of the surface streets to four lanes to handle some of the interstate traffic diverted off for the construction.

The third level flyovers used 8-foot deep, curved plate girders, spanning 250 feet. They sit on a hammer head substructure design, four on one bridge and five on the other. GIC used a 500-ton hydraulic crane to assist in the erection.

"Being a third level over two major interstates, it took extensive planning and sequencing," says Bryan Wilkerson, Senior Project Manager for Clarkson.

GIC did four separate weekend closures of I-435 or I-35 from Friday at 10 p.m. until Monday morning at 5 a.m. to erect the girders. The team faced penalties of $25,000 per hour, per direction if the interstates were not opened on time. GIC completed all four of them with time to spare.

Choosing Design-Build

The project is the largest let by KDOT and the state's first one using the design-build delivery method. The legislature authorized one design-build project to see how it would work. KDOT will submit detailed reports about the project.

"It's been a learning experience for KDOT," Gripka says.

GIC had experience with design-build. But Wilkerson reports it required a conscious effort to bring all of the parties together as a team, maintain transparency and reach consensus about how to address challenges.

"There are a lot of unknowns, uneasiness, giving up control the owner is used to," Wilkerson says.

All of the entities co-located in the same project office, which helped foster communication, as did daily meetings. GIC held cookouts, World Series watch parties, softball games and bowling parties to let team members get to know each other on a more personal level.

"That helped mold the teamwork concept," Wilkerson recalls. "And it's a fast-track time frame that demanded a tremendous amount of hours from all team members."

GIC started construction while the engineers continued to work on final designs for the later portions of the job. GIC fully integrated the job, with shared responsibility for all aspects of the work.

"Design-build works on a project that's fairly complicated and big enough in scope that you can put the various pieces together," Gripka says. "Being able to move it up and getting the job built is the real benefit."

The Advantages of Diverging Diamond Interchange      

One of the final phases of the project is construction of a diverging diamond interchange at I-35 and 95th Street. Traffic will move to the left side of the road between the interchange ramps. Those coming from the east and heading northbound on I-35 can turn right onto the interstate and those going southbound cross the intersection and then flow left onto the interstate. Through 95th Street traffic will cross back to the right side of the road.

"You are not turning across traffic when you take your left," Gripka says.

The project also includes construction of bridges over the frontage roads and moving existing utilities. The interchange is closed during construction.

"Diverging diamonds work really well when you construct them in places with a lot of left turning movements," Gripka says. "In this situation with all of the turning movements, it should move traffic quicker."

In addition to improving efficiency of the interchange, construction time and cost are shortened, because the width of the bridge is narrower without the need for a left turn lane. With fewer conflict points, the diverging diamond interchange can improve safety.

Gripka reports that at the diverging diamond in Springfield, Missouri, motor vehicle accidents are down 30 percent and injury accidents down 60 percent.

The diverging diamond will be completed within six months. If the interchange was not closed, the project would have taken a year. GIC will complete a subphase early to open a frontage road for access to retailers.

Keeping Traffic Flowing

While the diverging diamond required closing the intersection, most of the work has taken place while maintaining traffic flow. KDOT placed restrictions on closures. A lot of paving took place on weekdays between 9 a.m. and 3 p.m. and weekends to avoid rush hour traffic, since one lane was closed to allow entry and exit of the trucks.

"This was a big puzzle on the construction phasing and sequencing, and very linear, finishing one aspect of work before starting on the next," Wilkerson says. "The challenge was how do we combine different pieces of the puzzle, so we could do them at the same time. The team members worked well together and were thinking outside the box to move the phasing and trade durations of certain closures to come up with an equal or better solution."

The project remains on budget and on track for completion in December.

Gripka reports a decrease in accidents during construction and no fatalities. The team meets weekly to discuss issues. HNTB is advising KDOT on safety. KDOT also has one person assigned to monitoring lane drops.

KDOT is using a system to electronically monitor traffic, stranded cars and accidents. Gripka says the tools make it easier to head off issues.  

"The public has accepted the job and they are not severely impacted," Gripka concludes. "They see the improvements and work going on. It's been well received. That's something to be proud of."